Apparatus for producing refractory metal



Sept l5, 1959 o. w. MoLEs ETAL 24,904,491

APPARATUS vFOR PRODUCING REFRACTORY METAL Filed ay 2. 1956 2 Sheets-Sheet l AGE/VT Sept. 15, 1959 o. w. MoLEs ETAL APPARATUS FoRPRonucING REFRACTORY METAL 2 Sheets-Sheet 2 Filed May 2. 1956 United States Patent APPARATUS FOR PRODUCING REFRACT'DRilI METAL Oliver W. Moles, Plainfield, NJ., and Leonard W. Gendvil, Dongan Hills, N.Y., and Howard R. Palmer, Henderson, Nev., assignors to National Laad Company, New York, N.Y., a corporation of New Jersey Application May 2, 1956, Serial No. 582,131 2 Claims. (Cl. y204-246) The present invention relates in general to the electrolytic production of titanium metal and more particularly to an improved electrolytic cell for producing titanium metal of high purity and ductility.

Various thermal and chemical methods are known for producing titanium metal by converting titanium halides to the pure metallic state. Chemical methods for producing titanium metal usually involve the reduction of a titanium halide, such as titanium tetrachloride, by reacting the halide with a reducing metal such as an alkali or alkaline earth metal or magnesium (Kroll Patent No. 2,205,854) followed by reco-very of the titanium metal by multiple operations including vacuum distillation, leaching, and compacting the metal for purposes of are melting.

While titanium metal has been made in appreciable quantities by various thermal and chemical methods, these methods are, in general, expensive and diicult to practice and the resulting metal is frequently contaminated with impurities such as oxygen or nitrogen which, even in very small amounts, tend to impair or destroy some of the most important physical properties of the metal and in particular its ductility. Pure titanium metal is highly ductile and hence suitable for a great many applications in industry whereas titanium metal contaminated with even small amounts of oxygen or nitrogen is hard, its ductility being so impaired by the oxygen and nitrogen as to render the metal ill-suited for commercial use.

An object, therefore, of this invention is to provide superior means for producing substantially pure highly ductile titanium metal from titanium halides economically.

A further object is to provide a superior electrolytic cell for producing titanium metal of high ductility and on a commercial scale by electrolysis of titanium halides in a basket-like cathode immersed in a molten salt bath.

Another object of the invention is to provide an improved cathode for use in an electrolytic cell for producing titanium metal directly from titanium halides wherein maximum yields of titanium metal are obtained and substantially all of the titanium metal is deposited as substantially pure relatively large particles.

These and other objects of the instant invention will become apparent from the following more complete description thereof and the accompanying drawings in which:

Figure l is a vertical elevation, partly in section, of the improved electrolytic cell of the present invention for producing titanium metal on a commercial scale;

Figure 2 is a section taken on line 2 2 of Figure l;

Figure 3 is a section taken on line 3 3 of Figure l; and

Figure 4 is an enlarged broken vertical section of the improved cathode used in the cell shown in Figure 1 showing details of the composite supporting means of the cathode.

The electrolytic cell of the instant invention is one charice it" l g t,

2 acterized by its simplicity of design, its economy of oper-- ation and the production of high quality titanium metal on a commercial scale, the latter attribute being achieved by providing the cell with superior sealing means including a protective atmosphere above the electrolyte.

More particularly, the present invention relates to an electrolytic cell which is sealed against the admission of deleterious gases and has a cathode in the lform of a basket in which titanium metal is deposited as relatively large crystals of high quality and ductility, the cathodic basket being cooperatively associated with a cooling hood whereby the basket may be withdrawn with its deposit of titanium metal from the cell for subsequent cooling without exposing the titanium metal in the basket to the atmosphere prior to recovery.

Before describing the features of the improved cell of this invention, it may facilitate an understanding and appreciation of these features to point out at the outset that the cell is adapted to produce titanium metal by electrolysis of a titanium halide, such Ias titanium tetrachloride, in a fused salt bath comprising one or more of the chlorides, bromides or iodides of alkali metals, alkaline earth metals and magnesium or mixtures thereof, the .titanium halide being introduced into the electrolyte below the surface thereof and confined within a cathodic basket-like member immersed in the electrolyte by simultaneously passing-direct current through the fused salt bath at a rate synchronized with the titanium halide addition such that the amount of current added is sulcient to reduce the titanium halide to metal within the basket, any reduced titanium halides, if present, being retained wholly within the basket.

Referring now to Figure 1, the cell body is indicated generally at 10 and comprises an outer shell 11 formed of iron or other suitable metal; an inner shell 12 also formed of iron or other suitable metal; and suitable insulating brick as indicated at 13 and 14 respectively. The brick 13 between the outer shell 11 and the inner shell 12 is preferably a high quality Crucible brick, and the brick 14 which is used to line the inner face of the inner shell 12 and to form the electrolyte retaining chamber 15 of the cell is preferably a high grade aluminum oxide brick.

Referring again to Figure 2, the electrolyte chamber 15 of the cell is shown as rectangular in cross-section and in the instant embodiment of the invention its length is substantially twice its width. At opposite ends of the electrolyte chamber 15 are anodes 16-16, each anode being recessed into the corresponding end wall of the electrolyte chamber 15 adjacent the bottom thereof. Suitable electrical connections (not shown) are made to the respective anodes and to the cathode, hereinafter described, for passing current through the electrolyte in the manner well known in the art. In addition to the anodes 16-16, the cell is also provided with a plurality of heating electrodes for heating the fused salt electrolyte and maintaining it in a molten condition at a predetermined temperature during the production of the titanium metal. In the present embodiment of the invention, the heating electrodes comprise graphite bars, indicated generally at 17, set into the refractory brick lining of the electrolyte chamber on opposite sides respectively thereof, each heating electrode extending from the top of the cell downwardly to a point adjacent the bottom of the electrolyte chamber. Each heating electrode 17 is connected by suitable electrical connections (not shown) to a power source for delivering current to the heating electrodes.

Referring to Figure l, it will be seen that the upper open end of the electrolyte chamber 15 is provided with a metal closure-member V18 having a depending metal collar 19 arranged to fit snugly in the open upper end of the electrolyte chamber. The closure-member 18 is retained in the open upper end of the electrolyte chamber by means of a lip extending laterally from the collar 19 and adapted to rest on the rim of the electrolyte chamber to form a tight seal therewith. The closure-member 18 is formed of iron, stainless steel or other suitable metal and is provided with a centrally located substantially rectangular opening 20, the width and length of the opening 20 being of sufficient dimensions to permit the cathode including the composite cathode supporting means, hereinafter described, to readily pass therethrough. Referring to Figure 4, the center aperture 21B of the closure-member 18 is circumscribed by an upstanding collar 21 which constitutes one wall of a U- shaped channel 22 formed on the upper surface of the closure-member 18 and circurnscribing the base of the collar 21, the second wall of the channel 22 being formed by an upstanding metal flange 23 spaced outwardly laterally from the collar 21. The upstanding flange 23 also serves as the inner wall of a second or outer channel 24 which circumscribes the rst or inner channel 22, the outer wall of the outer channel 24 comprising an upstanding metal ange 25 similar to the metal flange 23. These two channels 22 and 24 respectively are adapted to contain a low melting point metal which is frozen during operation of the cell so as to provide gas-tight seals. respectively, for a metal cover-plate 26, which is adapted to cover the openingr 20 of the closure member 18; and for a cooling hood 27.

Referring to Figure 4, the metal cover plate 26 is substantially rectangular and formed with depending side and end flanges 28 and 29 which are adapted to engage in the inner channel 22 when the cover plate 26 is seated over the opening 20; and to be sealed in the frozen metal therein during electrolysis to exclude air, oxygen or the like from entering the chamber 15.

The cooling hood 27 comprises a substantially rectangular metal shell or casing closed at its upper end and open at its bottom end; and is adapted to be supported above the cell in a manner such that the hood may be displaced vertically to and from the opening 20 of the electrolyte chamber 15. Thus, during operation of the ycell the cooling hood 27 is adapted to be held in a raised position relative to the cell, as indicated by the full lines in Figures l and 4. Upon completion of any given run the cooling hood 27 is adapted to be lowered onto the closure member 18 of the cell. as idicated by the broken linesv in Figures l and 4, in which position the edges of the open bottom end of the cooling hood are sealed in the metal in the outer channel 24 to form a gas-tight seal. When the hood is in this position the cathode. including its composite supporting means, is adapted to be drawn up into the hood to cool the deposit of titanium metal before exposing it to the atmosphere. The overall height of the cooling hood 27 is thus somewhat greater than the overall length of the cathode and its composite supporting means, whereby the latter, which is sometimes referred to hereinafter as the cathode assembly and which comprises the cover-plate 26, the cathodic basket 38 and its supporting means, may be drawn upwardly out of the chamber 15 into the cooling hood. Cooling is effected by providing the cooling hood with a jacket 30 through which a coolant such as water is circulated by means of pipes 31 and 32.

In order to raise the cathode assembly into the cooling hood, the top plate 33 of the cooling hoodis provided with a central aperture through which a lift rod 34 may be introduced to be detachably connected to the cover plate 26 as hereinafter described. In addition, a feed pipe 35 is provided in the lower end of the cooling hood for introducing an inert gas such as argon into the cooling hood while a pipe 36 is provided in the top plate 33 of the cooling hood for bleeding olf the gases from the hood.

As mentioned above, the cooling hood 27 is adapted to be raised and lowered as indicated by the dotted lines in Figure 1 relative to the closure member 18 of the cell, and to this end the hood is shown provided with suitable eye bolts or the equivalent for attaching the hood to suitable hoisting means (not shown). Similarly, the lift rod 34 is provided `at its upper end with an eye or equivalent means by which the lift rod may be attached to suitable hoisting means for raising the cathode assembly into the cooling hood. In this connection, the cover-plate 26 of the cell is provided with a metal yoke member 37 having an internally threaded aperture at the center of its span in which the lower end of the lift rod 34 is adapted to be threadedly engaged thereby to detachably connect the latter to the cover plate 26.

Figure 4 shows the detailed construction of the cathode assembly. The cathodic basket of this assembly is indicated at 3S and comprises two imperforate sheet metal side walls, two perforated sheet metal side walls, an imperforate bottom and an irnperforate top plate 39, a suitable type of metal being iron, nickel alloys or titanium. Although the construction shown and the arrangement of the basket in the cell with its two perforated side Walls opposite the anodes 16-16 is preferred, it will be understood that these are not critical limitations. Moreover, the top plate 39 may be formed integrally with the side and end walls of the basket but preferably the body of the basket is separable from the top plate 39, being detachab-ly connected thereto by bolts arranged at the upper edges of the sides and ends of the basket for fastening the latter to apertured tongues depending from the underside of the top plate 30. This construction facilitates recovery of the titanium metal deposit from the basket.

Turning now to the supporting means of the basket, the former comprises a multi-tube structure which is shown especially well in Figure 4. In this embodiment of the invention, the innermost tube 4i) of the multi-tube structure is a nickel tube connected at its upper end by an elbow to a feed pipe 41 adapted to feed titanium tetrachloride, from a source not shown, in the interior of the basket within the electrolyte. It will be noted, however, that the lower end of the nickel tube does not extend all the way into the basket but is provided adjacent the underside of the top plate 39 of the basket with a coupling 42 by which the lower end of the nickel feed tube 40 is connected to the upper end of a tube 43 made of titanium metal or other suitable refractory metal which extends from the coupling 42 down into the interior of the cathode basket 38. The titanium metal extension 43 of the nickel feed tube 4t) was found expedient in commercial operations in order to avoid bridging of titaniumnickel sponge at the lower end of the nickel feed tube. Moreover, in order to protect the titanium metal extension 43, the latter is provided with a graphite tube lining 44 which extends from the lower end of the titanium metal extension 43 upwardly into the nickel tube 40, the graphite liner terminating therein at a point somewhat above the top plate 39 of the basket.

As will be seen from Figure l, the basket is adapted to be wholly immersed in the electrolyte, and consequently the composite supporting means of the basket is immersed in the electrolyte and also exposed to the inert atmosphere above the surface of the electrolyte. Since it is not expedient to attempt to support the entire weight of the cathodic basket including the titanium metal deposit therein by means of the nickel feed tube 40, a pipe of greater strength such'as the ironv pipe 45 is adapted to be telescoped over the nickel feed tube 40 and welded at its lower end to the top 39 of the basket, the upper end of the basket supporting pipe 45 being threadedly engaged in a circular flange 46 supported by the coverplate 26 of the chamber 15. Inasmuch as the iron pipe 45 would be attacked by the fused salt electrolyte, the pipe 45 is surrounded on both its inner and outer sides by concentric nickel tubes 47 and 48, each nickel tube being Welded at its lower end t0 the top 39 of the basket and threadedly engaged at its upper end in the central aperture of a circular metal flange 49 and 50 respectively superposed on the cover-plate V26 of the chamber 15, each flange being insulated therefrom and from iron pipe 45 by electrical insulating gaskets. In this respect it is important to mention that if the nickel tubes 47 and 48 are not insulated electrically from the current carrying iron pipe 45, suflicient voltage drop would occur between the upper and lower ends of the nickel tubes to cause electrochemical destruction of these tubes.

The upper end of the inner nickel sleeve 47 extends above the flange 49 to accommodate a cap 51 into which the upper end of the nickel feed tube 40v is threadedly engaged, the cap 51 serving as the sole support for the nickel feed tube 40, the lower end of which passes freely through an -aperture in Ithe top plate 39 of the basket. Referring again to the nickel tubes 47 and 48 for protecting the iron pipe 45, the latter is shown insulated from the nickel tubes by suitable heat insulation such as, for example, aluminum oxide or Ithe like. As a final protection against `the corrosive effects of the inert atmosphere above the bath, the outer nickel tube 48 is surrounded by a graphite sleeve 52 which is telescoped over the outer nickel tube 48, the graphite sleeve being supported on the top 39 of the basket with the upper end of the graphite sleeve terminating at a point immediately beneath the underside of the cover-plate 26 of the cell. This entire assembly, i.e. the nickel feed pipe 40, the iron pipe 45 and the two concentric nickel sleeves which protect the iron pipe 45 extends through an aperture in the cover-plate 26 of the cell, the tubes 45, 47 and 48 being secured thereon bythe aforesaid circular anges 46, 49 and 50, and fastening means indicated generally at 53. The aforesaid electrical insulating gaskets of the flanges 49. and 50 serve also to insure substantially air-tight seals between the respective flanges and the cover plate of the cell. Moreover, the flange 46 of the iron pipe 45 is provided with a metal bracket 54 to which is connected a lead 55 of a power source for supplying current to the electrolyte, the current conductor from the lead to the basket being the iron pipe 45; and with suitable cooling means indicated generally at 56 comprising a copper tube welded to the peripheral edge of the flange 46 and adapted to be supplied with a coolant such as water.

As previously stated, it is necessary to protect the titanium metal deposit from oxygen or other deleterious gases and to this end a suitable protective atmoshpere is provided above the surface of the electrolyte. Suitable protective gases for this purpose include inert gases such as argon or helium which may be introduced into the chamber by pipe 59. A chlorine outlet pipe 57 may be provided to bleed cd chlorine and other gases from the cell.

The fused salt electrolyte 58 used in this and other cells of this type comprises preferably a molten halide salt of an alkali or alkaline earth metal including magnesium, particularly the chlorides of the metals which may be employed singly or in combination. Mixtures of these halides which form low melting point eutectics are most convenient to employ such as, for example, mixtures of sodium chloride and strontium chloride, sodium chloride and lithium chloride, sodium chloride and barium chloride, sodium chloride and magnesium chloride or mixtures thereof.

The operation of the cell may be described briefly as follows. Titanium tetrachloride vapor is fed into the cell through the nickel feed pipe 40 which, by its graphite lined titanium metal extension 43, discharges the TiCl4 into the electrolyte below the surface thereof and within the confines of the basket 38. At 4the same time electric current is passed through the cell by way of the electrical lead 54 connected to the iron tube 45 which supports the cathodic basket, through the electrolyte to the anodes 16-16, the current being passed thro-ugh the cell at a rate synchronized with the rate of TiCl4 addition so that in effect the reduction of the titanium values to titanium metal takes place within the basket with substantially no migration of titanium values throughout the remaining portion of the electrolyte. A theoretically suicient current will comprise about four faradays of electricity passed concurrently through the cell which introduces approximately one mole of TiCl4 into the cell. In actual practice, however, it has been found desirable to add a quantity of electricity somewhat in excess of the theoretical amount in order to provide for cell losses, variations in cell design, ctc. With .the type of cell shown herein, it has been found desirable to add from about 4.5 to 7.9 faradays of electricity per mole of TiCl.,= introduced in order to maintain e'lcient cell operation.

In order to illustrate the effectiveness of the improved electrolytic cell of this invention for the production of highly ductile titanium metal on a commercial scale, the following example is given.

Example I Using a cell similar to that shown in .the drawings, a fused salt electrolyte comprising 700 lbs. of sodium chloride was added to Vthe cell chamber 15 and heated to a temperature of 850 C. In the preferred operation of `the cell the sodium chloride used was first purified. This may. be done in either of two Ways. Thus, prior to the introduction of the titanium tetrachloride direct current may be passed between a cathodic rod (introduced temporarily into the cell) and the anodes 16-16 for a predetermined period of time; or by making a relatively short run using the cathodic basket and TiCl., to produce Ititanium metal which is discarded.

' Titanium tetrachloride in vapor form .was thereafter introduced into the electrolyte below the surface thereof and Within the confines of the basket at the rate of 1.85 lbs. per hour. Concurrently, a direct electric current equivalent to 6.35 faradays per mole of TiCl4 introduced was passed through the cell. In order to obtain substantially 6.35 faradays per mole of 'IiCl4 introduced, 750 amperes with an impressed voltage of approximately 7.0 volts was required. This Was board voltage, the voltage between the anodes and the cathodic basket at melt level being about 4.1 volts. The cell varied from about 2.4 volts to about 2.9 volts.

The cathodic basket was rectangular as shown in the drawings, the perforated sides opposite the anodes 16-16 being 9 inches by 15 inches with 1A inch holes spaced 1/2 inch on centers, the imperforate sides being l2 inches by 15 inches. Both the bottom and top of the basket were solid and measured 9 by 12 inches. The cathode current density based on the overall area of the perforated sides was 0.54 ampere per square centimeter.

The run was continued for a period of 83.5 hours using a protective atmosphere above the bath, after which time the introduction of TiCl4 vapors was stopped. Thereafter, the cooling hood was lowered over the electrolyte chamber and the cathode basket and its supporting means were lifted up out of the chamber 15 into the cooling hood without exposing the titanium metal in the basket to the atmosphere. The titanium metal was deposited in the basket on the inner surfaces of the perforated walls in the form of an irregular mass of large ductile crystals. Upon removal from the basket, the titanium metal deposit was leached and the resulting metal weighed 38 pounds which corresponds to a yield of substantially 98% of the original titanium values added as TiCl4. The hardness of the metal was less than BHN.

From the foregoing example it will be apparent that the improved cell of this invention is capable of producing a high quality titanium metal on a commercial scale.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof and the present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changesV which' come within the meaning and range of equivalency of the claims are, therefore, intended to be embraced therein.

We claim:

1. A cathode assembly for an electrolytic cell for producing a refractory metal by electrolysis of a refractory metal halide in a fused salt electrolyte comprising in combination: a performated metal basket having an apertured cover; means to support said basket in said cell compris ing a tubular electrical conductor, fastening means arranged to connect the lower end of said tubular electrical conductor to said basket cover over the aperture therein and a current carrying member at the upper end of said tubular electrical conductor arranged to support the latter in `said cell, and to connect the upper end of said electrical conductor to a cathode current source; a feed pipe arranged to extend through said tubular electrical conductor into said basketto feed a refractory metal halide therein; and protective means for said tubular electrical conductor to preclude electrolytic disintegration thereof said protective means comprising a pair of metallic sleeves arranged concentric to said electrical conductor and in laterally spaced relationship thereto one of said sleeves being inside of said tubular electrical conductor and the second sleeve outside thereof, fluid tight fastening means arranged to connect the lower end of each sleeve to the cover of said basket and electrical insulation arranged at the upper end of each sleeve to insulate its upper end from said tubular electrical conductor.

2. In an electrolytic cell for producing a refractory metal by electrolysis of a refractory metal halide in a chamber containing a fused salt electrolyte, anodes at opposite walls the upper open end of said chamber arranged to seal of said chamber, an imperforate cover over 3 said chamber from the atmosphere and a cathode assembly in said chamber comprising a perforated metal basket having anapertured cover, and ajfeed pipe arranged to feed a refractory metal: halide into said basket the improvernentcomprising;.meansV to support said basket in said chamber comprising a tubular electrical conductor, fastening `rne'ans arranged to connect the lower end of said tubular electrical conductor to said basket cover over the aperture therein and' a current carrying member at the upper end'of said tubular electrical conductor arranged to support the latter in said chamber, and to connect the upper end'of said electrical conductor to a cathode current source; and protective means for said tubular electrical conductor to preclude electrolytic disintegration thereof said protective means comprising a 4pair of metallic sleeves arranged concentric to said electrical conductor and in laterally spaced relationship thereto one of said sleeves' being inside said tubular electrical conductor and the second sleeve outside thereof; fluid tight fastening means arranged to connect the lower end of each sleeve to the cover of said basket; and electrical insulation'arranged at the upper end of each sleeve to insulate its upper end from said tubular electrical conductor.

References Cited in the ijle of this patent UNITED STATES PATENTS 2,502,888 Ravenscroft Apr. 4, 1950 2,542,989 Carter et al Feb. 27, 1951 2,712,523 Alpert et al July 5, 1955 2,749,295 Svanstrom et al. June 5, 1956 2,801,964 Opie et al. Aug. 6, 1957 FOREIGN PATENTS 682,919 Great Britain Nov. 19, 1952 744,396 Great Britain Feb. 8, 1956 

1. A CATHODE ASSEMBLY FOR AN ELECTROLYTIC CELL FOR PRODUCING A REFACTORY METAL BY ELECTROLYSIS OF A REFRACTORY METAL HALIDE IN A FUSED SALT ELECTROLYTE COMPRISING IN COMBINATION: A PERFORMATED METAL BASKET HAVING AN APERTURED COVER; MEANS TO SUPPORT SAID BASKET IN SAID CELL COMPRISING A TUBULAR ELECTRICAL CONDUCTOR, FASTENING MEANS ARRANGED TO CONNECT THE LOWER END OF SAID TUBULAR ELECTRICAL CONDUCTOR TO SAID BASKET COVER OVER THE APERTURE THEREIN AND A CURRENT CARRYING MEMBER AT THE UPPER END OF SAID TUBULAR ELECTRICAL CONDUCTOR ARRANGED TO SUPPORT THE LATTER IN SAID CELL, AND TO CONNECT THE UPPER END OF SAID ELECTRICAL CONDUCTOR TO A CATHODE CURRENT SOURCE; A FEED PIPE ARRANGED TO EXTEND THROUGH SAID TUBULAR ELECTRICAL CONDUCTOR INTO SAID BASKET TO FEED A REFRACTORY METAL 